1. Field of the Invention
The invention relates to a fault-tolerant approach to monitoring and intervening with an implantable device in the neurological biosignaling of human patients suffering from disorders such as epilepsy and locked in syndrome. More particularly, the invention relates to a hardware redundancy based fault-tolerant multielectrode array for use with a brain implantable device for monitoring and intervening in the treatment of epilepsy or locked-in syndrome.
2. Description of the Related Art
Epilepsy is one of the most common neurological disorders, affecting 0.4% to 1% of the world's population. Sander J W A S: ILAE Commission Report The epidemiology of the epilepsies: Future directions. Epilepsia, 38(5):614-618, 1997. Pharmacology, the first line of treatment for epilepsy, is helpful for controlling seizures in approximately 64% of patients. Kwan P, Brodie M J: Early identification of refractory epilepsy. New England Journal of Medicine, 342(5):314-319, 2000. For the remaining approximately 10-20 million patients worldwide with uncontrolled seizures a second line of treatment, where available, is brain surgery [Engel J: Surgical treatment for epilepsy. JAMA: The Journal of the American Medical Association, 300(21):2548-2550, 2008.], and a third line of treatment which has emerged in recent years is the use of brain implantable devices [Fisher R S: Therapeutic Devices for Epilepsy, Annals of Neurology, 71(2):157-168, 2012]. Currently brain implantable devices employ electrical stimulation to control seizures. Fisher R S, Handforth A: Reassessment: Vagus nerve stimulation for epilepsy. Neurology, 53(4):666, 1999; Fisher R, Salanova V, Witt T, et al.: Electrical stimulation of the anterior nucleus of thalamus for treatment of refractory epilepsy. Epilepsia, 51(5):899-908, 2010; Morrell M, RNS System Pivotal Investigators: Results of a multicenter double blind randomized controlled pivotal investigation of the RNS system for treatment of intractable partial epilepsy in adults. Annual Meeting of the American Epilepsy Society (AES), 2009.
Other implantable devices under development seek to warn of an impending seizure, deliver drugs locally or cool the brain to control seizures. Epilepsy surgery may require multi-day intracranial monitoring of the brain to locate the source of seizures and brain implantable devices to control seizures require permanent monitoring of brain activity to detect or predict a seizure.
Parallel to this effort in epilepsy is an independent effort to develop a brain machine interface (BMI) to detect brain activity and typically activate an external actuator such as a robotic arm or make a decision. Lebedev M A, Nicolelis M A L: Brain machine interfaces: past, present and future. Trends in neurosciences, 29:536-546, 2006. In the BMI field the effort is primarily focused on detection and analysis of single unit or multi-unit activity and to a lesser extent on the measurement and analysis of the local field potential. Though there are differences between the epilepsy and BMI fields, there are also similarities in that both fields endeavor to measure neuronal activity directly from the brain and increasingly for a long period of time up to the life of the patient. There is also mounting evidence that the sensing solution in these efforts will involve increasingly larger numbers of electrode contacts which are often placed in a dense arrangement. Baker M: From promising to practical: tools to study networks of neurons. Nature Methods, 7(11):877-883, 2010. Rubehn B, Bosman C, Oostenveld R, et al.: A MEMS-based flexible multichannel ECoG-electrode array. Journal of Neural Engineering, 6(3):109-118, 2009.
The currently available as well as the proposed solutions for continuous real-time sensing of the electrical activity of the brain are all intolerant to faults. Lanning B, Joshi B, Kyriakides T, Spencer D, Zaveri H: Emerging technologies for brain implantable devices. Epilepsy: The Intersection of Neurosciences, Biology, Mathematics, Physics and Engineering, 2011. Edited by: Osorio I, Zaveri H P, Frei M G, Arthurs S. CRC Press. There are several aspects of an implantable sensing device which can fail. These include the reference electrode, sensors, signal conditioning and digitization circuitry, and computation, power and communication sub-systems. Faults which affect sensing can arise because of sensor failure due to mechanical stress on the sensor or the connecting wires during surgery to place electrodes or due to stress from changes in the brain and the surrounding milieu thereafter. Sensor failure can also arise because the foreign body response of the brain can result in encapsulation of a sensor due to gliosis. In case of erroneous behavior of the implanted sensors, the electrical activity at the site of the failed electrode contact will not be observed correctly, thereby impairing the purpose of the implanted device. For epilepsy surgery this may require the approximation of information from neighboring sensors if they exist. In the case of a seizure control device the failure of error free monitoring of the electrical activity of the brain may necessitate surgery to remove faulty sensors and implantation of a new set of sensors. While the initial surgery to place sensors carries a risk, surgery to replace sensors and a device can involve further risk with associated morbidity and mortality which remain to be determined but is expected to be equal to or greater than that of the surgery to place the first set of sensors.
It is the inventors' belief that reliable sensing of the human brain for an extended period of time necessitates fault-tolerant multielectrode array design to assure multielectrode array reliability. That is, fault-tolerance must be incorporated into the device architecture. Accordingly, the present invention provides two hardware redundancy based fault-tolerant solutions to manage intermittent and permanent faults. A permanent fault is one which exists indefinitely in absence of a corrective action while an intermittent fault is one which appears and disappears repeatedly.
The present invention overcomes the deficiencies of prior systems, method and apparatuses by providing a brain implantable device composed of one or more multielectrode sensing arrays with fault-tolerant mechanisms. Two different embodiments are disclosed in accordance with the present invention for the provision of such a multielectrode array. The first embodiment is composed of rows or columns of spare sensor modules on the edge of or within the sensor grid of the multielectrode array. In accordance with the second embodiment, spare sensor modules in the multielectrode array are based on a defined geometry (interstitial redundancy). A reconfiguration solution is provided for both the spare row or column and the interstitial redundancy solutions. Finally, the efficacy of the present solutions is demonstrated through analytical and simulation determinations of the reliability of multielectrode arrays designed with row or column or interstitial redundancy.